﻿using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

public class DynamicMethodExecutor
{
    private Func<object, object[], object> m_execute;

    public DynamicMethodExecutor(MethodInfo methodInfo)
    {
        this.m_execute = this.GetExecuteDelegate(methodInfo);
    }

    public object Execute(object instance, object[] parameters)
    {
        return this.m_execute(instance, parameters);
    }

    private Func<object, object[], object> GetExecuteDelegate(MethodInfo methodInfo)
    {
        // parameters to execute
        ParameterExpression instanceParameter =
            Expression.Parameter(typeof(object), "instance");
        ParameterExpression parametersParameter =
            Expression.Parameter(typeof(object[]), "parameters");

        // build parameter list
        List<Expression> parameterExpressions = new List<Expression>();
        ParameterInfo[] paramInfos = methodInfo.GetParameters();
        for (int i = 0; i < paramInfos.Length; i++)
        {
            // (Ti)parameters[i]
            BinaryExpression valueObj = Expression.ArrayIndex(
                parametersParameter, Expression.Constant(i));
            UnaryExpression valueCast = Expression.Convert(
                valueObj, paramInfos[i].ParameterType);

            parameterExpressions.Add(valueCast);
        }

        // non-instance for static method, or ((TInstance)instance)
        Expression instanceCast = methodInfo.IsStatic ? null :
            Expression.Convert(instanceParameter, methodInfo.ReflectedType);

        // static invoke or ((TInstance)instance).Method
        MethodCallExpression methodCall = Expression.Call(
            instanceCast, methodInfo, parameterExpressions);

        // ((TInstance)instance).Method((T0)parameters[0], (T1)parameters[1], ...)
        if (methodCall.Type == typeof(void))
        {
            Expression<Action<object, object[]>> lambda =
                Expression.Lambda<Action<object, object[]>>(
                    methodCall, instanceParameter, parametersParameter);

            Action<object, object[]> execute = lambda.Compile();
            return (instance, parameters) =>
            {
                execute(instance, parameters);
                return null;
            };
        }
        else
        {
            UnaryExpression castMethodCall = Expression.Convert(
                methodCall, typeof(object));
            Expression<Func<object, object[], object>> lambda =
                Expression.Lambda<Func<object, object[], object>>(
                    castMethodCall, instanceParameter, parametersParameter);

            return lambda.Compile();
        }
    }
}
